1. Field of the Invention
The present invention relates to a wireless communication apparatus, and more particularly, to a multiple antenna communication apparatus.
2. Description of the Related Art
Traditional wireless communication apparatuses use a single antenna at the transmitting end to emit electromagnetic waves for the transmission of communication signals. Traditional wireless communication apparatuses to also use a single antenna at the receiving end to receive the signals carried by the electromagnetic waves. However, with the progress of communication algorithms and manufacturing techniques of integrated circuits, wireless communication apparatuses no longer use a single antenna as the device for transmitting and receiving electromagnetic waves.
Multi-input and multi-output (MIMO) wireless communication apparatuses utilize multiple antennas for transmitting and receiving electromagnetic waves. Exhibiting spatial diversity, MIMO wireless communication apparatuses have higher throughput and longer transmission distance than traditional wireless communication apparatuses without sacrificing transmission bandwidth or increasing power consumption. Due to the features listed above, MIMO wireless communication apparatuses are now used in a majority of all wireless communication systems.
When designing a wireless communication apparatus, it is common to dispose an antenna device at an antenna region of a printed circuit board of a radio frequency (RF) circuit. To evenly distribute ground voltage, traditional RF circuits usually dispose as many main ground vias as possible in the open space of the printed circuit board. FIG. 1 shows a layout of a printed circuit board of a conventional two-antenna communication apparatus 100. As shown in FIG. 1, the conventional two-antenna communication apparatus 100 comprises an RF printed circuit board 110, which includes four layers, and a plurality of main ground vias 140 penetrating the four layers and evenly distributed on the RF printed circuit board 110. The RF printed circuit board 110 comprises a first antenna device 120 and a second antenna device 130. The first antenna device 120 is disposed at an antenna region on the first layer. The second antenna device 130 is disposed at an antenna region on the fourth layer.
Wireless communication apparatuses usually require high radiant efficiency. For MIMO wireless communication apparatuses, isolation degree between antennas significantly affects radiant efficiency. As customers nowadays demand smaller consumer electronic devices, all types of wireless communication apparatuses have to follow the trend such that the distance between antennas disposed on the wireless communication apparatus is reduced. As a result, the isolation degree between such antennas is diminished.
To solve the problem of the reduction of the isolation degree between antennas, it is common to attach an open transmission line between the feed points of two antennas, or to remove a part of the printed circuit board to create a slot between the feed points of two antennas. FIG. 2 shows the attachment of an open transmission line between the feed points of the two antennas 120 and 130 of the two-antenna communication apparatus 100 shown in FIG. 1. As shown in FIG. 2, the first antenna device 120 and the second antenna device 130 are respectively disposed on the left and right sides of the antenna region of the RF printed circuit board 110 to increase the isolation degree between the first antenna device 120 and the second antenna device 130. An open transmission line with length equal to one-fourth the wavelength of the emitted electromagnetic wave of the two-antenna communication apparatus 100 is further attached to the two-antenna communication apparatus 100 between the feed points of the two antennas 120 and 130. As a result, the isolation degree between the first antenna device 120 and the second antenna device 130 is further improved.
FIG. 3 shows the removal of a part of the printed circuit board 110 of the two-antenna communication apparatus 100 shown in FIG. 1. As shown in FIG. 3, the first antenna device 120 and the second antenna device 130 are respectively disposed on the left and right sides of the antenna region of the RF printed circuit board 110 to increase the isolation degree between the first antenna device 120 and the second antenna device 130. A part of the printed circuit board 110 between the feed points of the two antennas 120 and 130 is removed to create a slot with a length of one-fourth the wavelength of the emitted electromagnetic wave of the two-antenna communication apparatus 100. The slot does not contain any device or wire such that the isolation degree between the first antenna device 120 and the second antenna device 130 is further improved.
However, both solutions for improving the isolation degree between antennas provided above require additional board area or manufacture steps. Therefore, these solutions are not suitable when designing a wireless communication apparatus of small size, such as a universal serial bus (USB) device.
FIG. 4 shows a lateral view of the two-antenna communication apparatus 100 shown in FIG. 1. As shown in FIG. 4, the current path between the first antenna device 120 and the second antenna device 130 starts from a ground terminal of the first antenna device 120, passes through a main ground via 140 on the antenna region of the second layer of the printed circuit board 110, further passes through a main ground via 140 on the antenna region of the third layer of the printed circuit board 110, and ends at a ground terminal of the second antenna device 130. As shown in FIG. 4, the current path between the first antenna device 120 and the second antenna device 130 is too short such that the coupling effect between the between the first antenna device 120 and the second antenna device 130 is too large for the first antenna device 120 and the second antenna device 130 to have an acceptable isolation degree.
Therefore, there is a need to design a novel layout structure for a printed circuit board of a multiple antenna communication apparatus such that the isolation degree and the radiant efficiency thereof can be improved without increasing the area of the printed circuit board.